Apparatus and Method for Detecting Fluid Entering a Wellbore

ABSTRACT

The method and apparatus of the present invention provides for detecting a flow of a formation fluid entering into a wellbore. An ultrasonic sensor is placed in a wellbore. The sensor has a resonant member that is exposed to a fluid in the wellbore. At a location in the wellbore, acoustic energy is measured wherein the acoustic energy is related to turbulence from formation fluid entering the wellbore. In another embodiment of the invention a tool is provided for detecting a flow of a formation fluid into a downhole location in a wellbore. The ultrasonic sensor has a resonant member that is adapted to be in contact with a fluid in the wellbore. The sensor generates electrical signals when exposed to ultrasonic turbulences caused by a formation fluid entering into the wellbore. A processor processes the electrical signals to detect the flow of the formation fluid entering into the wellbore.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/250,598, filed Oct. 14, 2005.

FIELD OF THE INVENTION

The invention relates generally to the field of the evaluation forhydrocarbons in a wellbore, and more specifically to a method andapparatus for detecting flow of formation fluids into wellbores.

BACKGROUND OF THE INVENTION

Downhole tools, such as wireline tools, bottom hole assemblies attachedto a drill string, each having a variety of sensors are commonlyutilized to determine a variety of parameters of interest relating thesubsurface formations, including detection of formation fluids flowinginto the wellbores. It is useful to detect the presence, extent, andlocation (depth) of the wellbore fluids entering a wellbore. Suchinformation may be utilized for completing the wells, performingremedial work and/or to determine one or more characteristics of thereservoir or the formation.

An increase in the demand of natural gas has led to the need to completelow volume gas wells. This demand has caused the oil and gas explorationindustry to identify small, low volume gas entering into the wellbores.These wells may be air drilled boreholes or drilled utilizing drillingfluid. It is thus useful to detect the presence and location of suchsmall gas producing zones.

Also, of importance is the detection of liquids into the wellboreswhether prior to completing such wells for producing hydrocarbons orafter completion. It is useful to detect whether a formation fluid isleaking into a wellbore after completion for remedial work. Acousticsensors, including ultrasonic sensors, carried by downhole tools havebeen utilized to detect formation fluid flows into the wellbores. Incertain downhole situations, fluid entering the wellbores through smallareas create turbulences in the wellbore fluid (which may be liquid orair) in the ultrasound frequency range. Ultrasonic sensors have beenutilized to detect such turbulence. Ultrasonic sensors utilizing apiezoelectric element have been utilized. Such sensors are enclosed inan outer casing which may be a metallic or a non-metallic (plastic,rubber, etc.) housing to protect the sensor from the boreholeenvironment (high pressure and temperature). These protective encasementtends to reduce the ability of the sensor to detect the ultrasonicturbulence due to the sound reflection and/or attenuation due to theprotective casing material.

Thus, it is desirable to have downhole tools that include ultrasonicsensors that have greater sensitivity and which are able to withstandthe downhole environment, i.e., high temperatures and high pressures(which may be greater that 300 degrees Fahrenheit and over 20,000 psi).The present invention provides an apparatus and method that address theabove-noted problems.

SUMMARY OF THE INVENTION

One aspect of the invention provides a method of detecting a flow of aformation fluid entering into a wellbore. An ultrasonic sensor is placedin a wellbore. The sensor has a resonant member that is exposed to afluid in the wellbore. The sensor is tuned to a resonant frequency andis pressure and temperature balanced for use in wellbore. Acousticenergy relating to turbulence from formation fluid entering the wellboreis measured utilizing the ultrasonic sensor. Signals from the sensor areprocessed to determine the presence of the formation fluid entering intothe wellbore and correlated with the location (depth) in the wellboreutilizing the sensor depth data obtained from the depth measurementsmade relating to the sensor location in the wellbore. The method alsoprovides utilizing a set of sensors arranged circumferentially a tool toobtain full coverage of measurements along the inner circumference ofthe wellbore. The method further provides for utilizing an additionalset of sensors longitudinally spaced from the first set to correlatedata to accurately determine the presence and location of the entry ofthe fluid into the wellbore.

In another embodiment of the invention a tool is provided for detectinga flow of a formation fluid at a downhole location in a wellbore. Thetool includes at least one ultrasonic sensor. The ultrasonic sensor hasa resonant member that is adapted to be in direct contact with thewellbore fluid. The ultrasonic sensor is tuned to a resonant frequencyand generates electrical signals when exposed to ultrasonic turbulencescaused by the formation fluid entering into the wellbore. A processorprocesses the electrical signals to detect the flow of the formationfluid entering into the wellbore. A temperature sensor carried by thetool measures the temperature of the wellbore fluid and the processorcorrelates the information from the temperature and the ultrasonicsensor to verify the detection of the formation fluid entering thewellbore.

The method and apparatus of the invention provides embodiments of themore important features of the invention have been summarized ratherbroadly in order that the detailed description thereof that follows maybe better understood, and in order that the contributions to the art maybe appreciated. There are, of course, additional features of theinvention that will be described hereinafter and which will form thesubject of the claims appended hereto.

BRIEF DESCRIPTION OF THE FIGURES

The present invention and its advantages will be better understood byreferring to the following detailed description and the attacheddrawings in which:

FIG. 1 illustrates a downhole tool for detecting fluids entering into awellbore according to one exemplary embodiment of the present invention;

FIG. 2 illustrates a section of a downhole tool for detecting acousticenergy in a wellbore;

FIG. 3 illustrates a cross-section of a section of a downhole tool thatshows a sensor and pressure compensation system in a tool body accordingto an exemplary embodiment of the present invention; and

FIG. 4 illustrates a cross-section of an acoustic sensor made accordingto an exemplary embodiment of the present invention.

While the invention will be described in connection with its preferredembodiments, it will be understood that the invention is not limitedthereto. It is intended to cover all alternatives, modifications, andequivalents which may be included within the spirit and scope of theinvention, as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In view of the above, the present invention through one or more of itsvarious aspects and/or embodiments is described to provide one or moreadvantages, such as noted below.

FIG. 1 illustrates a system 100 for detecting fluid flow into awellbore. The system 100 shows a downhole tool 100 placed in a wellbore110 utilizing a tool carrying member 112, which may be a wireline,tubing, slick line or any other suitable carrying member. The wellbore110 may contain air or a liquid, such as a drilling fluid or productionfluid, as a medium 118. The tool 102 is shown to include a loweracoustic sensor arrangement or set 120 and an upper acoustic sensorarrangement or set longitudinally spaced apart from the lower sensor setby a known distance. Each sensor arrangement may include multipleultrasonic sensors, each such sensor further may be an ultrasonicsensor. The sensors in each sensor arrangement may be placedcircumferentially around the tool 102 to provide a full coverage ofmeasurements around the borehole 110. In one aspect, the individualsensors each may provide a limited circumferential coverage. In such acase, several circumferentially spaced sensors, for example six orseven, may be utilized as sensor sets to provide the full coverage. Thestructure and operation of each such sensor and the sensor sets isdescribed in more detail below. The tool 102 further may contain atemperature sensor 130 that measures the temperature of the wellboremedium 118. The tool 102 is shown lowered into the wellbore via a pullyby a wireline 112 on a winch 117 placed on suitable carrier, such as atruck 115 (for land operations) or an offshore platform (for offshoreoperations). A computer system 150, that may include a processor 152 iscoupled to the tool 102 via power and data lines carried by theconveying member 112. The computer system 150 contains one or morememory storage devices, visual displays, other equipment, and computerprograms embedded on one or more computer readable media that isaccessible to the computers for performing the methods, operations andthe functions relating to the tool 102 according to the presentinvention.

Still referring to FIG. 1, a formation fluid 142 entering the wellboreat a location 143, in some instances, may cause or create turbulence inthe wellbore 110 in the ultrasonic frequency range. The sensors in eachsensor set 120 and 122, in one aspect, are tuned to a suitable frequencyto detect acoustic frequencies in the ultrasonic range. In one aspect,each individual sensor is tuned to approximately 40 KHz, although anyother frequency may be utilized. As the tool 102 is moved in thewellbore 110, for example, toward the surface, individual sensors insensor set 120 and 122 detect turbulence created by the fluid 142 in theultrasonic range, each sensor providing corresponding electricalresponses or signals. The signals from each such sensor or from multiplesensors in a set combined with each other may be processed to detect ordetermine the presence of the fluid 142 entering the wellbore 110.Similarly, the sensor set 120 provides signals responsive to theturbulence when the sensors in the set 120 are proximate to the fluidentry location 143. The data from the two sensor sets 120 and 122 may becorrelated to provide an accurate detection and determination of thelocation or depth of the fluid entry location 143. The processor 152 maybe disposed in the tool 102 or at the surface 115 or it may bedistributed.

FIG. 2 illustrates a section 200 of a downhole tool for detectingacoustic energy in a borehole. The section may be located in the upperor lower portion of downhole tool 102. This section of the tool 102contains circumferentiallly arranged portals 210 for housing ultrasonicsensors 220 within the portals. A separate portal is provided for eachsensor of a sensor set. The section 200 also includes a liquid fillopening 230. Enough portals may be provided so that full acousticcoverage of an inside circumference of the wellbore is enabled asdiscussed above with reference to FIG. 1. In one embodiment, two sets ofsensors, each set with seven portals with seven sensors may be used in adownhole tool, one set located in an upper tubular tool section andanother at a lower tubular tool section.

FIG. 3 illustrates a cross-section of the tool section illustrated inFIG. 2. Each ultrasonic sensor 220 is securely placed in itscorresponding portal within the tool housing 312. Referring also to FIG.4, which is an illustration of sensor 220, an outer surface 222 of aresonant member 224 of the sensor 220 is directly exposed to theenvironment outside of the tool during operation, i.e., when the tool isin the wellbore, the surface 222 is exposed to wellbore fluid. Thehousing 312 includes a conduit or fluid line 320 to provide fluidcommunication between a sensor cavity 226 and a flexible member 340. Theconduit 320 and the flexible member 340 provide pressure compensationfor the oil to expand or contract when the tool is downhole. The oilprovides for both temperature and pressure compensation as boreholeconditions change. The fluid line 320 and the sensor cavity 226 arefilled with a suitable light viscosity oil, such as silicone having adensity of less than 100 centistokes. Any other suitable liquid may alsobe utilized for the purpose of this invention.

FIG. 4 illustrates a cross section of an acoustic sensor 220 providedaccording to one embodiment of the invention. As noted above, sensor 220may be located within one of several portals around the downhole tool102. A housing 400, which may be made of tungsten, contains a membranemember 410, which has an outer surface 222 that is exposed to theoutside environment. The inner surface of the membrane is attached to apiezoelectric member 420, which may be a plate, by a suitable resin orby any other suitable material or technique. The membrane 410 with thepiezoelectric member 420 together form the resonant member 224 of thesensor 220. Electrodes 430 may be attached to the piezoelectric plate420 and to the sensor housing 400. An opening 440 to the cavity 226enables the fluid flow between the sensor and the flexible member viathe fluid line 320 to compensate for the pressure variations as the oilexpands or contracts in the wellbore. The housing 400 may have sealingmaterials 450 and fastening apparatus 460.

The resonant member 224 of sensor 220 may be tuned to be more or lesssensitive to different ranges by varying the diameter and thickness ofthe membrane member 410 as well as the piezoelectric plate 420. Thesetuning methods are well understood by practitioners in the art. Forexample, frequency ranges around 40 kilohertz are useful for thedetection of hydrocarbon fluid flow. A membrane member 410 of thicknessof about 0.020 inches with an appropriately adjusted piezoelectric plate420 may be used to form a sensor's resonant member that may provideadequate sensitivity in the acoustic frequency ranges useful forhydrocarbon fluid flow detection. The sensor 220 may also be tuned toany desired frequency in-situ utilizing electrical circuits. The sensormay be tuned to any desired frequency within a range of frequencies. Afeedback circuit may be provided that determines the desired frequencyand a processor tunes the sensor to that desired frequency. This methodallows for adjusting the resonant frequency as the downhole conditionschange. The exemplary, non-limiting, sensor 220 described herein isshown to include a singe resonant member directly exposed to thewellbore fluid, which sensor is tuned to a selected frequency in a rangeof frequencies, and which is further pressure compensated by a liquidmedium inside the sensor. Single membrane acoustic sensors sometimes arereferred in the art as unimorph mode or flexural mode tranducers. Othersensors, including but not limited to sensors having piezoelectricelements with impedance matching and directly in contact with thewellbore fluid may also be utilized. Such sensors are referred to asextensional mode or radial mode tranducers.

Thus, the present invention provides a method, apparatus and system fordetermining flow of a formation fluid entering into a wellbore. In onenon-limiting embodiment the invention provides a method that includesplacing an ultrasonic sensor that has a resonant member exposed to afluid in the wellbore and measuring, at a depth of the wellbore,acoustic energy related to turbulence caused by the formation fluidentering into the wellbore. A location of the formation fluid enteringthe wellbore from the detected turbulence is then determined.Temperature may also be measured at the location and the acoustic energyand temperature may be correlated to verify the location of the fluidentering the wellbore. The resonant member of the ultrasonic sensor maybe tuned to selected frequency ranges. Tuning may be accomplished byselecting dimensions of the resonant member (the thickness and diameterof the sensor membrane part as well the piezoelectric plate) thatdefines a selected resonant frequency or the ultrasonic sensor, or thetuning may occur by applying the sensor in-situ to an electric circuit.The tuning may be occur when the downhole tool is located within thewellbore. The resonant member of the ultrasonic sensor may be attachedto a housing adapted to contain a liquid and wherein the resonant memberfurther comprises a metallic membrane exposed to an outside environmentand a piezoelectric member that is protected from the outsideenvironment. The ultrasonic sensors may be located around a tubularmember to provide substantially a full acoustic coverage of an insidecircumference of the wellbore. The ultrasonic sensor may be tuned to afrequency of about 40 KHz. Pressure compensation may be provided to theultrasonic sensor when the ultrasonic sensor is in the wellbore.

In one embodiment, the invention provides an apparatus for detectingflow of a formation fluid into a wellbore at a downhole location. Theapparatus comprises at least one ultrasonic sensor carried by the tool,the ultrasonic sensor having a resonant member adapted to be in contactwith the borehole fluid. The ultrasonic sensor generates electricalsignals when exposed to ultrasonic turbulences caused by a formationfluid entering into the wellbore. A processor may be provided thatprocesses the electrical signals to determine location of the formationfluid entering the wellbore. The resonant member may be attached to ahousing that is adapted to contain a liquid therein to provide pressurecompensation to the resonant member when the tool is in the wellbore.The resonant member may have a membrane member and a piezoelectricmember attached to the membrane. The membrane may be a relatively thinmetallic member, such as titanium membrane about 0.020 inches thick. Theresonant member membrane may define a resonant frequency of theultrasonic sensor. A circuit may be utilized to tune the resonant memberto a selected resonant frequency. The resonant frequency of the resonantmember may be above the audio frequency, such as about 40 KHz. Theliquid in the sensor provides pressure compensation and may be made tobe in fluid communication with a liquid reservoir or with a flexiblemember that enables the liquid in the sensor to expand and contractdownhole. A plurality of ultrasonic sensors may be arranged around atubular member of the tool, and these sensors may provide substantiallyfull acoustic measurement coverage of an inside circumference of thewellbore. A temperature sensor may be provided that measures temperatureof the fluid in the wellbore and the processor may correlates themeasured temperature with the electrical signals to verify the locationof the fluid entering into the wellbore.

The embodiments described herein, therefore, are well adapted to carryout the invention. While various embodiments of the invention have beengiven for purposes of disclosure, numerous changes known to persons ofskill in the art may be made to practice the invention and to accomplishthe results contemplated herein, without departing from the concept orthe spirit of the invention. Various modifications will be apparent tothose skilled in the art. It is intended that all such variations thatare within the scope and spirit of the appended claims be embraced bythe foregoing disclosure.

1. (canceled)
 2. An acoustic sensor comprising: a resonant member havinga first side exposed to an outside environment; and a cavity configuredto enclose a second side of the resonant member and to house a liquidtherein to provide pressure compensation for the resonant member.
 3. Theacoustic sensor of claim 1, wherein the resonant member comprises amembrane coupled to a piezoelectric element.
 4. The acoustic sensor ofclaim 3, wherein the first side of the resonant member is a first sideof the membrane and the piezoelectric element is coupled to a secondside of the membrane.
 5. The acoustic sensor of claim 4, wherein themembrane is made at least in part from a metallic element.
 6. Theacoustic sensor of claim 3 further comprising an electrode coupled tothe piezoelectric element configured to provide a signal when themembrane is exposed to pressure vibrations.
 7. The acoustic sensor ofclaim 1 further comprising a fastener configured to fasten the acousticsensor into a tool housing.
 8. An apparatus, comprising: a housingconfigured for use in a wellbore; an acoustic sensor placed in thehousing, the acoustic sensor comprising: a resonant member having afirst side exposed to an outside environment, and a pressurecompensating device in fluid communication with a second side of theresonant member configured to provide pressure compensation for theresonant member.
 9. The apparatus of claim 8, wherein the pressurecompensating device comprises: a fluid reservoir in fluid communicationwith a flexible member on a first end thereof and the second side of theresonant member on a second end thereof.
 10. The apparatus of claim 9,wherein the fluid reservoir is sealed and filled with a fluid thatprovides the pressure compensation to the resonant member.
 11. Theapparatus of claim 8, wherein the resonant member includes a metallicmember and a piezoelectric element.
 12. The apparatus of claim 11further comprising an electrical connection coupled to the resonantmember configured to receive signals therefrom in response to appliedpressure on the resonant member.
 13. The apparatus of claim 12 furthercomprising a processor configured to process the signals received fromthe resonant member.
 14. The apparatus of claim 13 comprising aconveying member configured to convey the housing into the wellbore. 15.The apparatus of claim 14, wherein the processor is located at one of:(i) in the housing; and (ii) at a surface location configured to receiveinformation relating to the signals from the acoustic sensor via acommunication associated with the conveying member.